Elevators are complex machines. Interlocks help insure proper elevator operation. One of the interlocks ensures that the elevator door is opened only when the elevator is present or during maintenance operations. At a minimum, an elevator door interlock includes a sensor, that senses whether the door is open or closed, and a locking mechanism, that locks the door in the closed position.
Elevator door interlocks should have a housing that protects the parts from outside interference. Current housings are made from stamped pieces of sheet metal. The components of the interlock must be mounted to the housing. The current solutions are to attach mountings to the housing via welding, soldering, screws, bolts, or similar devices or means. It takes considerable time and skill to assemble a housing in this manner. Furthermore, the assembly is prone to breakage because of the large number of parts that are used.
Elevator door interlock housings are typically sheet metal formed into 5 sides of a box type enclosure and a cover, making up the sixth side, completes the enclosure. The covers currently used are simple squares or rectangles of sheet metal. Components of the interlock can be attached to the cover as they are to the housing, bringing along similar problems. The inconvenience of attaching parts to the sheet metal cover usually leads to the cover being merely a cover and otherwise not a part of the elevator door interlock structure.
The sheet metal solutions used for housings and covers also require that any text that should be on the housing or cover to be added as part of a separate operation. That separate operation is usually painting, printing, or affixing an adhesive backed label. These are poor solutions because, over the life of the unit, they wear off.
Elevator doors typically open to the left or to the right. The elevator door interlocks currently used are designed only for left opening or right opening doors. As such, elevator maintenance organizations must stock both the left and right opening varieties. Furthermore, repairmen must go into the field with the correct unit and have the risk of arriving at the job site with the wrong one.
Elevator door interlocks must have a mechanism for locking the door closed and releasing the door when it is proper to do so. The solution is usually to mount a locking fixture to the door that mates with a locking fixture in the elevator door interlock. The elevator door interlock is then mounted to the doorframe. When the door is shut, the two locking fixtures engage. Another part in the interlock housing controls merely engaging the locking fixtures or locking them together. In modern elevators, the controlling part is usually a solenoid. A solenoid, a mechanism wherein an actuator remains in a default position until electrical current is applied causing the actuator to move to an energized position, is well known in the art of electromechanical devices and particularly in the art of elevator door interlocks. Solenoids require a specified electrical current or voltage for proper operation. For example, a 24-volt DC solenoid requires a steady voltage of approximately 24 volts. Alternating current or too low a voltage would not work. Too high a voltage could destroy the solenoid. Furthermore, keeping a solenoid energized for long periods of time can cause the device to overheat and fail. Once again, repairmen must arrive at the job site with elevator door interlocks that match the electrical power used at that job site.
Elevator door interlocks often keep the solenoid energized when the door is unlocked. This shortens solenoid life.